You have the following inequality:
y ≥ -3x +4
In order to graph the previous inequality, you graph the corresponding equation of a line, which is given by:
y = - 3x + 4
the graph is all region above the previous line, because the inequality stablishes that all values greater than -3x + 4 (that is, the line) are solution.
Then, you have:
all red region in the previous graph contains the valid values of the inequality.
The limit of the region is the equation of the line.